In order to prevent from damage of the umbrella when it occurs upward wind, there are some designs with double covers on the frame of the umbrella, which can release pressure for avoiding the ribs of the frame being unusually folded and broken. As shown in FIG. 1, it can be seen that a prior known windproof umbrella includes a main rib (1) extending outsides from the upper notch (11) and being covered with an upper cover (12). A second rib (13) is pivoted on the main ribs (1) at a middle bottom position, while a lower cover (14) is covered on the second rib (13). A stretcher (15) has the outer end to pivot with the second rib (13). When the upward wind occurs, the main rib (1) and the second rib (13) are capable of changing the related position by the wind pressure and the airflow can pass through between the two covers (12), (14). The drawback of this umbrella is that the main rib (1) only extends to the board of the upper cover (12). The lower cover (14) is supported by the second only. The strength of the umbrella is thus not enough that the second rib (13) might be easily broken by the wind pressure.
As shown in FIG. 2, it shows another windproof umbrella with a single main rib (2) to increase the strength of the umbrella. The lower cover (21) covers the area from the pivoted position of the main rib (2) and a stretcher (22) to an end (23) of the main rib (2). The upper cover (24) covers a notch (25) and the middle place of the frame of the umbrella and has a plurality of connectors (26) on the board to connect a related end (23) of the main rib (2) with a wire (27). It is to be understood that a gap exists between the two covers for releasing the pressure of the upward wind. The drawback of the design is that the upper cover (25) is connected with the end (23) of the main rib (2) by the wires (27) only and the strength of the umbrella is still not enough for avoiding damage.